Cathode material and non-aqueous electrolyte secondary battery using it

ABSTRACT

The present invention relates to a negative electrode material for non-aqueous electrolyte secondary batteries, characterized in that the negative electrode material comprises a composite particle including solid phases A and B, the solid phase A being dispersed in the solid phase B, and the ratio (I A /I B ) of the maximum diffracted X-ray intensity (I A ) attributed to the solid phase A to the maximum diffracted X-ray intensity (I B ) attributed to the solid phase B satisfies 0.001≦I A /I B ≦0.1, in terms of a diffraction line obtained by a wide-angle X-ray diffraction measurement of the composite particle. This negative electrode material is capable of suppressing of pulverization thereof due to repeated cycles. Further, the use of this negative electrode material allows production of a non-aqueous electrolyte secondary battery having a high capacity and an excellent cycle life characteristic.

TECHNICAL FIELD

The present invention relates to a non-aqueous electrolyte secondarybattery to be used for portable information terminals, portable electricappliances, home use compact power storage devices, automatictwo-wheeled vehicles having motors as power sources, electric cars,hybrid electric automobiles and the like. More specifically, the presentinvention relates to a negative electrode material for non-aqueouselectrolyte secondary batteries.

BACKGROUND ART

Lithium secondary batteries, which have recently been utilized as mainpower supplies of mobile communication devices and potable electricappliances, are characterized by having high electromotive force and ahigh energy density.

Lithium secondary batteries in which lithium metal is used as a negativeelectrode material has a high energy density, but dendrite deposits on anegative electrode during charging. As charge/discharge are repeated,the dendrite develops to penetrate a separator and comes into contactwith a positive electrode, causing an internal short circuit. Further,as having a large surface area, the deposited dendrite has a highreactivity and reacts, on the surface thereof, with a solvent in anelectrolyte to form a solid-electrolytic interface layer having poorelectronic conductivity. This leads to higher internal resistance withinthe battery and to the existence of particles isolated from theelectronically conductive network. For these reasons, a charge/dischargeefficiency decreases.

Lithium secondary batteries in which lithium metal is used as a negativeelectrode material therefore have problems of low reliability and shortcycle life.

As an alternative negative electrode material for lithium metalcurrently used has been a carbon material capable of absorbing anddesorbing lithium ions, and batteries using this for the negativeelectrode thereof have come into practical use. There normally occurs noproblem of an internal short circuit due to dendrite in a negativeelectrode using a carbon material since metallic lithium does notdeposit thereon. However, the theoretical capacity of graphite, one ofcarbon materials, is 372 mAh/g, which is as small as about one tenth ofthe theoretical capacity of Li metal.

As other negative electrode materials known is a elemental metallic ornon-metallic material, which form a compound with lithium. In the caseof silicon, tin and zinc, for example, the compositions of therespective compounds with the largest content of lithium are Li₂₂Si₅,Li₂₂Sn₅ and LiZn. With lithium contained in this degree in each of thecompounds, metallic lithium usually does not deposit, to cause noproblem of the internal short circuit due to dendrite. Electrochemicalcapacities obtained by the change from elemental substances to thesecompounds are, respectively, 4199 mAh/g, 993 mAh/g and 410 mAh/g, whichare all larger than the theoretical capacity of graphite.

As a negative electrode material using a different compound from thosedescribed above, Japanese Laid-Open Patent Publication No. Hei 7-240201proposes a silicate of non-iron metal including a transition element.Further, Japanese Laid-Open Patent Publication No. Hei 9-63651 proposesa compound which comprises an intermetallic compound containing theGroup 4B elements, and at least one of P and Sb, and whose crystalstructure is any of CaF₂ type, ZnS type and AlLiSi type.

However, the aforesaid negative electrode materials with highercapacities than those of carbon materials have problems as describedbelow.

Simple substance metals and simple substance non-metals, which form acompound with lithium, have inferior charge/discharge cyclecharacteristics to carbon materials. The reason for that is presumed asfollows.

For example, silicon contains 8 silicon atoms in the crystallographicunit lattice thereof (cubic, space group Fd-3m). From a lattice constant“a”=0.5420 nm determined are a unit lattice volume of 0.1592 nm³ and avolume per one silicon atom of 19.9×10⁻³ nm³. Judging from the phasediagram of the silicon-lithium binary type, it is considered that, whensilicon electrochemically reacts with lithium at room temperature toform a compound, two phases, silicon and the compound Li₁₂Si₇, coexistin the initial stage of the reaction. Li₁₂Si₇ contains 56 silicon atomsin the crystallographic unit lattice thereof (rhombic, space groupPnma). From lattice constants “a”=0.8610 nm, “b”=1.9737 nm and“c”=1.4341 nm, a unit lattice volume of 2.4372 nm³ and a volume per onesilicon atom (a value obtained by dividing the unit lattice volume bythe number of the silicon atoms in the unit lattice) of 43.5×10⁻³ nm³are determined. Hence conversion from silicon to the compound Li₁₂Si₇causes an increase in volume by 2.19 times and the material thusexpands. When the reaction proceeds in such a state as the two phases,silicon and the compound Li₁₂Si₇, coexist, silicon partly converts intothe compound Li₁₂Si₇ and a large volume difference therebetween causesserious distortion of the material. This material is thereforeconsidered as prone to cracking and pulverizing.

Moreover, as the electrochemical reaction between silicon and lithiumadvances, the compound Li₂₂Si₅ with the largest content of lithium isultimately obtained. Li₂₂Si₅ contains 80 silicon atoms in thecrystallographic unit lattice thereof (cubic, space group F23). From alattice constant “a”=1.875 nm determined are a unit lattice volume of6.5918 nm³ and a volume per one silicon atom (a value obtained bydividing the unit lattice volume by the number of the silicon atoms inthe unit lattice) of 82.4×10⁻³ nm³. Hence conversion from silicon to thecompound Li₂₂Si₅ causes an increase in volume by 4.14 times, and hencethe material expands significantly. In the discharge reaction of thenegative electrode material, on the other hand, lithium is graduallyreduced from the compound, and the material thus shrinks. It istherefore considered that a major variation in material volume duringcharging/discharging brings about significant distortion of thematerial, whereby cracking occurs to pulverize particles.

It is further considered that, as spaces are formed among the pulverizedparticles to cause segmentation of the electronically conductivenetwork, a portion incapable of being involved in the electrochemicalreaction increases to deteriorate the charge/discharge characteristic.

Tin contains 4 tin atoms in the crystallographic unit lattice thereof(tetragonal, space group I41/amd). From lattice constants “a”=0.5820 nmand “c”=0.3175 nm, a unit lattice volume of 0.1075 nm³ and a volume perone tin atom of 26.9×10⁻³ nm³ are determined. Judging from the phasediagram of the tin-lithium binary type, it is considered that, when tinelectrochemically reacts with lithium at room temperature to form acompound, two phases of tin and the compound Li₂Sn₅ coexist in theinitial stage of the reaction. Li₂Sn₅ contains 10 tin atoms in thecrystallographic unit lattice thereof (tetragonal, space group P4/mbm).From lattice constants “a”=1.0274 nm and “c”=0.3125 nm, a unit latticevolume of 0.32986 nm³ and a volume per one tin atom (a value obtained bydividing the unit lattice volume by the number of the tin atoms in theunit lattice) of 33.0×10⁻³ nm³ are determined. Hence conversion from tinto the compound Li₂Sn₅ causes an increase in volume by 1.23 times andthe material thus expands.

Moreover, as the electrochemical reaction between tin and lithiumadvances, the compound Li₂₂Sn₅ with the largest content of lithium isultimately obtained. Li₂₂Sn₅ contains 80 tin atoms in thecrystallographic unit lattice thereof (cubic, space group F23). From alattice constant “a”=1.978 nm determined are a unit lattice volume of7.739 nm³ and a volume per one tin atom (a value obtained by dividingthe unit lattice volume by the number of the tin atoms in the unitlattice) of 96.7×10⁻³ nm³. Hence conversion from tin to the compoundLi₂₂Si₅ causes an increase in volume by 3.59 times, and hence thematerial expands significantly.

Zinc contains 2 zinc atoms in the crystallographic unit lattice thereof(hexagonal, space group P63/mmc). From lattice constants “a”=0.2665 nmand “c”=0.4947 nm, a unit lattice volume of 0.030428 nm³ and a volumeper one zinc atom of 15.2×10⁻³ nm³ are determined. Judging from thephase diagram of the zinc-lithium binary type, when zincelectrochemically reacts with lithium at room temperature to formseveral compounds, the compound LiZn with the largest content of lithiumis ultimately obtained. LiZn contains 8 zinc atoms in thecrystallographic unit lattice thereof (cubic, space group Fd-3m). Fromlattice constants “a”=0.6209 nm determined are a unit lattice volume of0.2394 nm³ and a volume per one zinc atom (a value obtained by dividingthe unit lattice volume by the number of the zinc atoms in the unitlattice) of 29.9×10⁻³ nm³. Hence conversion from zinc to the compoundLiZn causes an increase in volume by 1.97 times and the material thusexpands.

In the case of using tin or zinc, as in the case of silicon, therefore,the volume variation in negative electrode material due to thecharge/discharge reaction is large and the variation continues in astate where the two phases with great volume differences coexist. Thisis considered as the cause of cracking of a material and pulverizationof the particles thereof. It is further thought that, as spaces areformed among the pulverized particles to cause segmentation of theelectronically conductive network, a portion incapable of being involvedin the electrochemical reaction increases to deteriorate thecharge/discharge characteristic.

That is to say, when a simple substance metal or a simple substancenon-metal, which forms a compound with lithium, is used for a negativeelectrode, the metal or non-metal suffers a large volume variation andtends to be pulverized. This presumably causes the inferiorcharge/discharge cycle characteristic to a negative electrode using acarbon material.

Other than the aforesaid simple substances, Japanese Laid-Open PatentPublication No. Hei 7-240201 proposes a silicate of non-iron metalincluding a transition element as a negative electrode material capableof improving the cycle life characteristic. In this publication providedare examples of batteries in which a silicate of non-iron metalincluding a transition element is used as a negative electrode materialand comparative examples of batteries in which lithium metal is used asa negative electrode material, and the charge/discharge cyclecharacteristics of the respective batteries are compared. It is thendisclosed that the charge/discharge characteristics of the batteries inthe examples are improved more than those of the batteries in thecomparative examples. By comparison with a battery in which naturalgraphite is used as a negative electrode material, however, the maximumincrease in battery capacity in the examples is only about 12%.

Although not definitely stated in the publication, therefore, thereappears to be no significant increase in capacity of the battery inwhich silicate of non-iron metal including a transition metal for thenegative electrode thereof is used, as compared with a battery in whichgraphite is used for the negative electrode thereof.

Further, Japanese Laid-Open Patent Publication No. Hei 9-63651 proposesa compound which comprises an intermetallic compound containing theGroup 4B element and at least one of P and Sb, and whose crystalstructure is any of CaF₂ type, ZnS type and AlLiSi type, as a negativeelectrode material capable of improving the cycle life characteristic.

It is disclosed that the charge/discharge cycle characteristic is moreimproved in an example where the aforesaid compound is used for thenegative electrode than in a comparative example where Li—Pb alloy isused for the negative electrode. It is further disclosed that a highercapacity is obtained in the example than in a case of using graphite forthe negative electrode.

However, the battery in the example exhibits a significant decrease indischarge capacity at 10th to 20th cycles, and even in the case of usingMg₂Sn, which is presumably the most favorable compound, the dischargecapacity decreases to about 70% of the initial capacity after about 20thcycles.

Furthermore, Japanese Laid-Open Patent Publication No. 2000-30703proposes a negative electrode material, comprising solid phases A and B,the solid phase A comprising at least one of silicon, tin and zinc asthe constituent element thereof, the solid phase B comprising a solidsolution or an intermetallic compound, containing one of silicon, tinand zinc as the constituent element of the solid phase A, and at leastone element selected from the group consisting of the elements of Group2, transition, Group 12, Group 13, and Group 14 which are listed in LongForm of Periodic Table, with carbon excluded from Group 14 element. Itis disclosed that a battery using this negative electrode material forthe negative electrode thereof has a higher capacity and a more improvedcycle life characteristic than a battery using graphite for the negativeelectrode thereof.

When the crystallinity of the solid phase A in this material is high, aproblem may arise that stress within particles at the time of absorbinglithium concentrates in one direction to make the particles prone todestruction, leading to a shorter cycle life.

A description is given to crystallinity. In general, the crystalproperties are largely classified into amorphousness (in a state where adiffraction line is not obtained in a wide-angle X-ray diffractionmeasurement), micro-crystalline, poly-crystalline and mono-crystalline.For solving the aforesaid problems required is to lower thecrystallinity of the solid phase A. That the solid phase A in alow-crystallinity state here means that the solid phase A is in a mixedstate of amorphousness and micro-crystalline. It is to be noted thatmicro-crystalline means poly-crystalline with a crystal size of notlarger than about 150 nm. Further, the crystallinity of the solid phaseB may be poly-crystalline or micro-crystalline.

In order to solve the aforesaid problems, an object of the presentinvention is to provide a negative electrode material capable ofsuppressing pulverization thereof due to repeated cycles. Another objectof the present invention is to provide a non-aqueous electrolytesecondary battery having a high capacity and an excellent cycle lifecharacteristic, by the use of this negative electrode material.

DISCLOSURE OF INVENTION

A negative electrode material for non-aqueous electrolyte secondarybatteries in accordance with the present invention is one capable ofabsorbing and desorbing lithium, characterized in that: the negativeelectrode material comprises a composite particle including solid phasesA and B, the solid phase A being dispersed in the solid phase B; thesolid phase A comprises at least one element selected from the groupconsisting of silicon, tin and zinc; the solid phase B comprises a solidsolution or an intermetallic compound, which contains the constituentelement of the solid phase A, and at least one element selected from thegroup consisting of the elements of Group 2, transition, Group 12, Group13 and Group 14 which are listed in Long Form of Periodic Table, exceptfor the constituent element of the solid phase A and carbon; and theratio (I_(A)/I_(B)) of the maximum diffracted X-ray intensity (I_(A))attributed to the solid phase A to the maximum diffracted X-rayintensity (I_(B)) attributed to the solid phase B satisfies0.001≦I_(A)/I_(B)≦0.1, in terms of a diffraction line obtained by awide-angle X-ray diffraction measurement of the composite particle.

Further, a negative electrode material for non-aqueous electrolytesecondary batteries in accordance with the present invention is onecapable of absorbing and desorbing lithium, characterized in that: thenegative electrode material comprises a composite particle includingsolid phases A and B, the solid phase A being dispersed in the solidphase B; the solid phase A comprises at least one element selected fromthe group consisting of silicon, tin and zinc; the solid phase Bcomprises a solid solution or an intermetallic compound, which containsthe constituent element of the solid phase A, and at least one elementselected from the group consisting of the elements of Group 2,transition, Group 12, Group 13 and Group 14 which are listed in LongForm of Periodic Table, except for the constituent element of the solidphase A and carbon; and the half width (W) (radian) of the maximum peakintensity of diffracted X-rays, attributed to the solid phase A,satisfies 0.001≦W≦0.1, in terms of a diffraction line obtained by awide-angle X-ray diffraction measurement of the composite particle.

It is preferable that the solid phase A comprises Si and Sn, and thesolid phase B comprises a solid solution or an intermetallic compound,which contains Cu and at least one of Sn and Si.

It is preferable that the solid phase B comprises CuSi₂ and Cu₆Sn₅.

It is preferable that the solid phase B comprises CuSi₂ and a solidsolution containing Cu and Sn.

It is preferable that the solid phase B comprises Cu₆Sn₅ and a solidsolution containing Cu and Si.

It is preferable that the solid phase B comprises a solid solutioncontaining Cu and Si, and a solid solution containing Cu and Sn.

It is preferable that the solid phase A comprises Si and the solid phaseB comprises a solid solution or an intermetallic compound, whichcontains Ti and Si.

It is preferable that the solid phase B comprises TiSi₂ having a crystalstructure of at least one selected from the group consisting of Cmcm andFddd.

Further, a non-aqueous electrolyte secondary battery in accordance withthe present invention comprises: a positive electrode capable of areversible electrochemical reaction of lithium, a non-aqueouselectrolyte comprising an organic solvent and a lithium salt dissolvedin the organic solvent, and a negative electrode comprising theaforesaid negative electrode material.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view illustrating a structure of a cylindricalnon-aqueous electrolyte secondary battery used in an example.

BEST MODE FOR CARRYING OUT THE INVENTION

A negative electrode material for non-aqueous electrolyte secondarybatteries in accordance with the present invention is one capable ofabsorbing and desorbing lithium, characterized in that: the negativeelectrode material comprises a composite particle including solid phasesA and B, the solid phase A being dispersed in the solid phase B; thesolid phase A comprises at least one element selected from the groupconsisting of silicon, tin and zinc; the solid phase B comprises a solidsolution or an intermetallic compound, which contains the constituentelement of the solid phase A, and at least one element selected from thegroup consisting of the elements of Group 2, transition, Group 12, Group13 and Group 14 which are listed in Long Form of Periodic Table, exceptfor the constituent element of the solid phase A and carbon; and theratio (I_(A)/I_(B)) of the maximum diffracted X-ray intensity (I_(A))attributed to the solid phase A to the maximum diffracted X-rayintensity (I_(B)) attributed to the solid phase B satisfies0.001≦I_(A)/I_(B)≦0.1, in terms of a diffraction line obtained by awide-angle X-ray diffraction measurement of the composite particle.

When I_(A)/I_(B) is 0.1 or less, the volume ratio of the crystal of thesolid phase A in one particle comprising the solid phase A and the solidphase B is small and thereby, even with lithium absorbed in the solidphase A, stress concentration in one direction is decreased, having theeffect of suppressing cracking of particles.

When I_(A)/I_(B) exceeds 0.1, however, the volume ratio of the crystalof the solid phase A in one particle increases and thereby, with lithiumabsorbed in the solid phase A, stress concentration in one directionbecomes larger, and it thus becomes difficult to suppress cracking ofparticles.

When I_(A)/I_(B) is less than 0.001, while cracking of particles can besuppressed, such a small volume ratio of the crystal of the solid phaseA in one particle causes lowering of the absolute specific volume of theparticle, resulting in a decrease in capacity per volume.

Further, the negative electrode material for non-aqueous electrolytesecondary batteries in accordance with the present invention is onecapable of absorbing and desorbing lithium, characterized in that: thenegative electrode material comprises a composite particle includingsolid phases A and B, the solid phase A being dispersed in the solidphase B; the solid phase A comprises at least one element selected fromthe group consisting of silicon, tin and zinc; the solid phase Bcomprises a solid solution or an intermetallic compound, which containsthe constituent element of the solid phase A, and at least one elementselected from the group consisting of the elements of Group 2,transition, Group 12, Group 13 and Group 14 which are listed in LongForm of Periodic Table, except for the constituent element of the solidphase A and carbon; and the half width (W) (radian) of the maximum peakintensity of diffracted X-rays, attributed to the solid phase A,satisfies 0.001≦W≦0.1, in terms of a diffraction line obtained by awide-angle X-ray diffraction measurement of the composite particle.

W is a peak width measured at intensity “2θ” which is half as large asthe maximum peak intensity of diffracted X-rays, which is attributed tothe solid phase A, and represented by a radian unit. It should be notedthat “θ” is an incident angle of X-rays.

When W is not larger than 0.1 radian, the crystal size of the solidphase A in one particle comprising the solid phase A and the solid phaseB is so small as to raise the plastic limit thereof, over which thesolid phase A would fracture, even with lithium absorbed in the solidphase A. This makes the solid phase A resistant to fracture and theparticles resistant to crack.

When W exceeds 0.1 radian, however, the crystal size of the solid phaseA in one particle becomes larger so as to lower the plastic limitthereof. For this reason, the solid phase A fractures due to absorptionof lithium, and the particle becomes prone to crack.

When W is smaller than 0.001 radian, the plastic limit is so high as tosuppress cracking of the particles. Since the boundary between the solidphase A and the solid phase B increases in one particle to causedeterioration in electronic conductivity, an amount to absorb Lidecreases.

In the first preferred embodiment of the present invention, the solidphase A comprises Si and the solid phase B comprises a solid solution oran intermetallic compound, which contains Ti and Si.

The use of silicon for the solid phase A can theoretically maximize anamount to absorb Li, allowing a higher capacity. Further, by the use oftitanium for the solid phase B, titanium is bonded to lithium to inhibitoxygen as an impurity, which impairs reversibility of lithium, frombonding to silicon.

Moreover, it is particularly preferable that the solid phase B comprisesthe intermetallic compound of TiSi₂. TiSi₂ may have a crystal structureincluding either/both Cmcm or/and Fddd.

It should be noted that, with regard to the diffraction peak of TiSi₂which is attributed to the crystal structure of Cmcm or Fddd as obtainedby a wide-angle X-ray diffraction measurement, one whose peak positionhas shifted to the high angle side or the low angle side is regarded asthe diffraction peak of TiSi₂ which is attributed to the crystalstructure of Cmcm or Fddd.

In the second preferred embodiment, the solid phase A comprises Si andSn, and the solid phase B comprises a solid solution or an intermetalliccompound, which contains Cu and and at least one of Sn and Si.

The use of Si and Sn for the solid phase A improves the electronicconductivity of the solid phase A; the use of Cu for the solid phase Bimproves the electronic conductivity of the solid phase B.

The solid phase B for example may be: CuSi₂ and Cu₆Sn₅; CuSi₂ and asolid solution containing Cu and Sn; Cu₆Sn₅ and a solid solutioncontaining Cu and Si; and a solid solution containing Cu and Si and asolid solution containing Cu and Sn.

It is preferable that the aforesaid composite particle is synthesized bythe mechanical alloying method.

As another method to prepare the composite particle considered can be amethod comprising: quenching and solidifying a melt having a nominalcomposition of elements each constituting the composite particle, by thedry spraying, wet spraying, roll quenching or rotating electrode method;and then heat-treating the resultant solidified matter at a lowertemperature than a solidus temperature of a solid solution or anintermetallic compound, which is determined from the nominalcomposition.

However, the mechanical alloying method is more effective than theaforesaid method conducted by heat treatment in the respect offacilitating control of the volume ratio of the crystal of the solidphase A and control of the size thereof.

In the mechanical alloying method, a melt having a nominal compositionof each element composed of a solid phase A and a solid phase B isquenched and solidified by the dry spraying, wet spraying, rollingquenching or rotating electrode method, to obtain a solidified matter tobe used. Further, a powder of each element composed of a solid phase Aand a solid phase B may be used as a starting material.

The content of the solid phase A in one particle of the compositeparticles comprising the solid phase A and the solid phase B ispreferably from 10 to 40 wt %, and more preferably from 15 to 35 wt %.

The combination of a negative electrode comprising the aforesaidnegative electrode material, a positive electrode capable of bringing areversible electrochemical reaction of lithium and a non-aqueouselectrolyte obtained by dissolving lithium salts in an organic solventenables production of a non-aqueous electrolyte secondary battery havinga high capacity as well as an excellent cycle life characteristic.

The negative electrode can for example be obtained by application of anegative electrode material mixture, comprising the aforesaid negativeelectrode material, a conductive agent, a binder and the like, on thesurface of a current collector.

The conductive agent used for the negative electrode may be anyelectronically conductive material; For example, graphite such asnatural graphite (flake graphite, etc.), artificial graphite andexpanded graphite; carbon blacks such as acetylene black, Ketjen black,channel black, furnace black, lamp black and thermal black; conductivefibers such as carbon fiber and metallic fiber, a metallic powder suchas a copper powder, and conductive organic materials such aspolyphenylene derivatives are preferred, and these materials may bemixed in use. Particularly preferred among them are artificial graphite,acetylene black and carbon fiber.

The amount of the conductive agent to be added is not particularlylimited, but it is preferably from 1 to 50 parts by weight, morepreferably from 1 to 30 parts by weight, relative to 100 parts by weightof the negative electrode material. Moreover, since the negativeelectrode material to be used in the present invention has an electronicconductivity, the battery can function without addition of theconductive agent.

As the binder used for the negative electrode, either a thermoplasticresin or a thermosetting resin may be employed. Preferred for exampleare polyethylene, polypropylene, polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVDF), styrene butadiene rubber, atetrafluoroethylene-hexafluoroethylene copolymer, atetrafluoroethylene-hexafluoropropylene copolymer (FEP), atetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), avinylidene fluoride-hexafluoropropylene copolymer, a vinylidenefluoride-chlorotrifluoroethylene copolymer, anethylene-tetrafluoroethylene copolymer (ETFE resin),polychlorotrifluoroethylene (PCTFE), a vinylidenefluoride-pentafluoropropylene copolymer, a propylene-tetrafluoroethylenecopolymer, an ethylene-chlorotrifluoroethylene copolymer (ECTFE), avinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, avinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylenecopolymer, an ethylene-acrylic acid copolymer or an Na⁺ ion-cross-linkedcopolymer thereof, an ethylene-methacrylic acid copolymer or an Na⁺ion-cross-linked copolymer thereof, an ethylene-methyl acrylatecopolymer or an Na⁺ ion-cross-linked copolymer thereof, and anethylene-methyl methacrylate copolymer or an Na⁺ ion-cross-linkedcopolymer thereof, and these materials may be mixed in use. Particularlypreferred among them are styrene butadiene rubber, polyvinylidenefluoride, an ethylene-acrylic acid copolymer or an Na⁺ ion-cross-linkedcopolymer thereof, an ethylene-methacrylic acid copolymer or an Na⁺ion-cross-linked copolymer thereof, an ethylene-methyl acrylatecopolymer or an Na⁺ ion-cross-linked copolymer thereof, and anethylene-methyl methacrylate copolymer or an Na⁺ ion-cross-linkedcopolymer thereof.

The current collector to be used for the negative electrode may be anyelectronically conductive material which does not cause a chemicalchange in a constituted battery. Preferred for example are stainlesssteel, nickel, copper, titanium, carbon, a conductive resin, and oneobtained by treating the surface of copper or stainless steel withcarbon, nickel or titanium. Among them particularly preferred are copperand copper alloy. It is preferable that the surface of the currentcollector is roughened by surface treatment. These materials can also beused after treating the surface thereof with oxidization. The currentcollector to be used is formed of foil, a film, a sheet, a net, apunched sheet, a lath body, a porous body, a foamed body or fibers.Although the thickness is not particularly limited, a current collectorwith a thickness of 1 to 500 μm is preferably used.

The positive electrode can for example be obtained by application of apositive electrode mixture, comprising a positive electrode material, aconductive agent, a binder and the like, on the surface of a currentcollector.

As the positive electrode material, a metallic oxide containing lithiumis used. As the examples thereof cited can be Li_(x)CoO₂, Li_(x)NO₂,Li_(x)MnO₂, Li_(x)Co_(y)Ni_(1-y)O₂, Li_(x)Co_(y)M_(1-y)O₂,Li_(x)Ni_(1-y)M_(y)O_(z), Li_(x)Mn₂O₄ and Li_(x)Mn_(2-y)O₄. It is to benoted that M is one element selected from the group consisting of Na,Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb and B. Further, X, Yand Z satisfy 0≦x≦1.2, 0≦y≦0.9, and 2.0≦z≦2.3, respectively. Moreover,the x value varies with charge/discharge.

As positive electrode materials other than the aforesaid compounds, itis possible to use a transition metal chalcogenide, vanadium oxide andthe lithium compound thereof, niobium oxide and the lithium compoundthereof, a conjugate polymer comprising an organic conductive material,a Chevrel phase compound, or the like. It is also possible to use amixture of a plurality of different positive electrode materials.Although the mean particle size of the positive electrode activematerial particle is not particularly limited, it is preferably from 1to 30 μm.

The conductive agent used for the positive electrode may be anyelectronically conductive material which does not cause a chemicalchange at a charge/discharge potential of the positive electrodematerial. For example, graphite such as natural graphite (flakegraphite, etc.), and artificial graphite; carbon blacks such asacetylene black, Ketjen black, channel black, furnace black, lamp blackand thermal black; conductive fibers such as carbon fiber and metallicfiber, fluorinated carbon, metallic powders such as an aluminum powder,conductive whiskers such as zinc oxide whisker and potassium titanatewhisker, a conductive metal oxide such as titanium oxide, and conductiveorganic materials such as polyphenylene derivatives are preferred, andthese materials may be mixed in use. Particularly preferred among themare artificial graphite and acetylene black. The amount of theconductive agent to be added is not particularly limited, but it ispreferably from 1 to 50 parts by weight, more preferably from 1 to 30parts by weight, relative to 100 parts by weight of the positiveelectrode material. In the case of carbon or graphite, in particular,the amount thereof to be added is preferably from 2 to 15 parts byweight per 100 parts by weight of the positive electrode material.

As the binder used for the positive electrode, either a thermoplasticresin or a thermosetting resin may be employed. Preferred for exampleare polyethylene, polypropylene, polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVDF), styrene butadiene rubber, atetrafluoroethylene-hexafluoroethylene copolymer, atetrafluoroethylene-hexafluoropropylene copolymer (FEP), atetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), avinylidene fluoride-hexafluoropropylene copolymer, a vinylidenefluoride-chlorotrifluoroethylene copolymer, anethylene-tetrafluoroethylene copolymer (ETFE resin),polychlorotrifluoroethylene (PCTFE), a vinylidenefluoride-pentafluoropropylene copolymer, a propylene-tetrafluoroethylenecopolymer, an ethylene-chlorotrifluoroethylene copolymer (ECTFE), avinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, avinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylenecopolymer, an ethylene-acrylic acid copolymer or an Na⁺ ion-cross-linkedcopolymer thereof, an ethylene-methacrylic acid copolymer or an Na⁺ion-cross-linked copolymer thereof, an ethylene-methyl acrylatecopolymer or an Na⁺ ion-cross-linked copolymer thereof, and anethylene-methyl methacrylate copolymer or an Na⁺ ion-cross-linkedcopolymer thereof, and these materials may be mixed in use. Particularlypreferred among these materials are polyvinylidene fluoride (PVDF) andpolytetrafluoroethylene (PTFE).

The current collector to be used for the positive electrode may be anyelectronically conductive material which does not cause a chemicalchange at a charge/discharge potential of the positive electrodematerial. Preferred for example are stainless steel, aluminum, titanium,carbon, a conductive resin, and one obtained by treating the surface ofaluminum or stainless steel with carbon or titanium. Among themparticularly preferred are aluminum and aluminum alloy. It is preferablethat the surface of the current collector is roughened by surfacetreatment. These materials can also be used after treating the surfacethereof with oxidization. The current collector to be used is formed offoil, a film, a sheet, a net, a punched sheet, a lath body, a porousbody, a foamed body, fibers or a non-woven fabric. Although thethickness is not particularly limited, a current collector with athickness of 1 to 500 μm is preferably used.

The electrode material mixture to be used for the positive electrode andthe negative electrode, in addition to the conductive agent and thebinder, may be exemplified by a filler, a dispersing agent, an ionicconductor, a pressure reinforcing agent, and other various additives.Any fibrous material which does not cause a chemical change in aconstituted battery can be used as the filler. Usually, a fiber made ofan olefin polymer like polypropylene or polyethylene, glass or carbon isused. The amount of the filler to be added is not particularly limited,but it is preferably not more than 30 parts by weight relative to 100parts by weight of the electrode material mixture.

As for the constitution of the positive electrode and the negativeelectrode, it is preferable that the respective faces of the negativeelectrode material mixture and the positive electrode material mixtureare opposed to one another.

The non-aqueous electrolyte comprises a non-aqueous solvent and alithium salt dissolved in the solvent.

As the non-aqueous solvent preferred for example are: cyclic carbonatessuch as ethylene carbonate (EC), propylene carbonate (PC), butylenecarbonate (BC) and vinylene carbonate (VC), linear carbonates such asdimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methylcarbonate (EMC), and dipropyl carbonate (DPC), aliphatic carboxylic acidesters such as methyl formate, methyl acetate, methyl propionate andethyl propionate, γ-lactones such as γ-butyrolactone, linear ethers suchas 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE) andethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and2-methyl tetrahydrofuran, and aprotic organic solvents such asdimethylsulfoxide, 1,3-dioxolane, formamide, acetamide,dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane,ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolanederivatives, sulfolane, methyl sulfolane,1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylenecarbonate derivatives, tetrahydrofuran derivatives, ethyl ether,1,3-propanesultone, anisole, dimethyl sulfoxide and N-methylpyrrolidone,and these may be mixed in use. Among them particularly preferred aremixtures of cyclic carbonate and linear carbonate, and mixtures ofcyclic carbonate, linear carbonate and aliphatic carboxylic acid ester.

The preferable example of the lithium salt may include LiClO₄, LiBF₄,LiPF₆, LiAlCl₄, LiSbF₆, LiSCN, LiCl, LiCF₃SO₃, LiCF₃CO₂, Li(CF₃SO₂)₂,LiAsF₆, LiN(CF₃SO₂)₂, LiB₁₀Cl₁₀, lithium lower aliphatic carboxylate,LiCl, LiBr, LiI, chloroboranlithium, lithium tetraphenyl borate, andimide, and these may be mixed in use. Among them, LiPF₆ is particularlypreferred.

As for the non-aqueous electrolyte, it is preferable that thenon-aqueous solvent comprises at least ethylene carbonate and ethylmethyl carbonate while the lithium salt comprises LiPF₆. Although theamount of the non-aqueous electrolyte to be added to the battery is notparticularly limited, an added amount, as necessary according to theamount of the positive electrode material or the negative electrodematerial and the size of the battery, can be applied. Although theamount of the lithium salt to be dissolved in the non-aqueous solvent isnot particularly limited, it is preferably from 0.2 to 2 mol/l. And theamount to be dissolved is more preferably from 0.5 to 1.5 mol/l.

In place of the aforesaid non-aqueous electrolyte, a solid electrolyteas described below can also be used. Solid electrolytes can beclassified into inorganic solid electrolytes and organic solidelectrolytes.

As the inorganic solid electrolyte used for example are nitride, halide,oxyacid salt, and the like of Li. In particular, Li₄SiO₄,Li₄SiO₄—LiI—LiOH, xLi₃PO₄—(1-x)Li₄SiO₄, Li₂SiS₃, Li₃PO₄—Li₂S—SiS₂ andphosphorus sulfide compounds are effectively used.

As the organic solid electrolyte used for example are polymer materialssuch as polyethylene oxide, polypropylene oxide, polyphosphazene,polyaziridine, polyethylene sulfide, polyvinyl alcohol, polyvinylidenefluoride, polyhexafluoropropylene, and the derivatives, the mixtures andthe complexes thereof.

It is further effective, for the purpose of improving the dischargecharacteristic and the charge/discharge cycle characteristic, thatanother compound be added into the electrolyte. For example, triethylphosphate, triethanolamine, cyclic ether, ethylene diamine, n-glyme,pyridine, triamide hexaphosphate, nitrobenzene derivatives, crownethers, the fourth ammonium salts, ethylene glycol, dialkyl ether, andthe like are used.

As the separator, an insulating micro-porous thin film having large ionpermeability and prescribed mechanical strength is used. It ispreferable that this film has the function of closing pores at a certaintemperature or higher so as to increase the resistance. Examples of aseparator with hydrophobic properties and resistance to an organicsolvent may include a sheet, non-woven fabric and woven fabric, whichare made of a glass fiber or an olefin polymer fiber containing at leastone selected from the group consisting of polypropylene andpolyethylene. The pore size of the separator is preferably within such arange that the electrode material, the binder, the conductive agent andthe like, which have separated from the electrode, do not permeate inthe separator. The preferable range of the pore size is from 0.01 to 1μm, for example. The separator normally used is one with a thickness of10 to 300 μm. Further, although the porosity of the separator isdetermined according to permeability of electrons and ions, a materialand a film thickness, a preferable porosity is normally from 30 to 80%.

It is also possible to constitute a battery in such a manner that apositive electrode material mixture and a negative electrode materialmixture contain a polymer material having been made to absorb and retaina non-aqueous electrolyte comprising a solvent and a lithium salt to bedissolved in the solvent, and a porous separator comprising the polymerwhich has absorbed and retained the non-aqueous electrolyte isintegrated with a positive electrode and a negative electrode. Thepolymer material may be one capable of absorbing and retaining anon-aqueous electrolyte. As the example thereof cited may be avinylidene fluoride-hexafluoropropylene copolymer.

To the type of the battery applicable is any type such as coin type,button type, sheet type, laminated type, cylindrical type, flat type,rectangular type, and large type for use in electric automobiles and thelike.

Furthermore, although the non-aqueous electrolyte secondary battery ofthe present invention is used for portable information terminals,portable electric appliances, home use compact power storage devices,automatic two-wheeled vehicles, electric automobiles, hybrid electricautomobiles and the like, the battery is not particularly limitedthereto.

In the following, the present invention is more specifically describedby means of examples. However, the present invention is not limited tothese examples.

EXAMPLE 1

(i) Production of Negative Electrode Material

In such a manner that a composite particle comprised 20 parts by weightof Sn as a solid phase A and 80 parts by weight of FeSn₂ as a solidphase B, a mixed powder of Sn and Fe was melted, and the resultant meltwas quenched to be solidified by the roll quenching method. After theobtained solid was introduced into a ball mill container, the containerwas installed in a planetary ball mill and mechanical alloying wasperformed with a rotating speed and the time for synthesis set at 2800rpm and 10 hours, respectively, to obtain a prescribed powder.Subsequently, the obtained powder was classified through a sieve intoparticles with a particle size of not larger than 45 μm so as to producea negative electrode material A2.

(ii) Production of Negative Electrode

75 parts by weight of the negative electrode material as thus obtainedwas mixed with 20 parts by weight of a carbon powder as a conductiveagent and 5 parts by weight of a polyvinylidene fluoride resin as abinder. The resultant mixture was dissolved in N-methyl-2-pyrrolidone togive slurry. This was applied on a negative electrode current collectormade of copper foil, which was dried and then rolled to obtain anegative electrode.

(iii) Production of Positive Electrode

85 parts by weight of a lithium cobaltate powder as a positive electrodematerial was mixed with 10 parts by weight of a carbon powder as aconductive agent and 5 parts by weight of a polyvinylidene fluorideresin as a binder. The resultant mixture was dissolved inN-methyl-2-pyrrolidone to give slurry. This was applied on a positiveelectrode current collector made of aluminum foil, which was dried andthen rolled to obtain a positive electrode.

(iv) Assembly of Battery

A vertical sectional view of a cylindrical battery in accordance withthe present invention was shown in FIG. 1

A positive electrode 1 and a negative electrode 2 were spirally rolledup with a separator 3 comprising polyethylene arranged therebetween toform an electrode assembly. This electrode assembly was housed in abattery case 4 with a lower insulating plate 5 provided at the bottomthereof. A positive electrode lead plate 10 was then taken out of thepositive electrode 1 to be connected to a sealing plate 6 equipped witha positive electrode terminal 9 and a safety valve 8. Subsequently, anon-aqueous electrolyte comprising a mixed solvent of ethylene carbonateand ethyl methyl carbonate in a volume ratio of 1:1 and 1.5 mol/l ofLiPF₆ dissolved in the mixed solvent was injected into the battery case4. This battery case 4 was sealed with the sealing plate 6 equipped witha gasket 7 on the periphery thereof to produce a cylindrical batteryhaving a diameter of 18 mm and a height of 650 mm.

EXAMPLE 2

Except that the time for synthesis by mechanical alloying was 15 hours,a negative electrode material A3 was produced on the same conditions asin Example 1. Further, except that the negative electrode material A3was used in place of the negative electrode material A2, a battery wasproduced in the same manner as in Example 1.

COMPARATIVE EXAMPLES 1 AND 2

Except that the time for synthesis by mechanical alloying was 3 and 20hours, the respective negative electrode materials A1 and A4 wereproduced on the same conditions as in Example 1. Subsequently, exceptthat the negative electrode materials A1 and A4 were used in place ofthe negative electrode material A2, the respective batteries wereproduced in the same manner as in Example 1.

EXAMPLES 3 AND 4

Except that a mixed powder of Sn and Fe was used in such a manner that acomposite particle comprised 25 parts by weight of Sn as a solid phase Aand 75 parts by weight of a solid solution of Fe and Sn as a solid phaseB, and that the time for synthesis by mechanical alloying was 10 and 15hours, the respective negative electrode materials A6 and A7 wereproduced on the same conditions as in Example 1. Subsequently, exceptthat the negative electrode materials A6 and A7 were used in place ofthe negative electrode material A2, the respective batteries wereproduced in the same manner as in Example 1.

COMPARATIVES EXAMPLES 3 AND 4

Except that the time for synthesis by mechanical alloying was 3 and 20hours, the respective negative electrode materials A5 and A8 wereproduced in the same conditions as in Example 3. Further, except thatthe negative electrode materials A5 and A8 were used in place of thenegative electrode material A2, the respective batteries were producedin the same manner as in Example 1.

EXAMPLES 5 AND 6

Except that a mixed powder of Si and Co was used in place of the mixedpowder of Fe and Sn, in such a manner that a composite particlecomprised 15 parts by weight of Si as a solid phase A and 85 parts byweight of CoSi₂ as a solid phase B, and that the time for synthesis bymechanical alloying was 10 and 15 hours, the respective negativeelectrode materials B2 and B3 were produced on the same conditions as inExample 1. Subsequently, except that the negative electrode materials B2and B3 were used in place of the negative electrode material A2, therespective batteries were produced in the same manner as in Example 1.

COMPARATIVE EXAMPLE 5 AND 6

Except that the time for synthesis by mechanical alloying was 3 and 20hours, the respective negative electrode materials B1 and B4 wereproduced in the same conditions as in Example 5. Further, except thatthe negative electrode materials B1 and B4 were used in place of thenegative electrode material A2, the respective batteries were producedin the same manner as in Example 1.

EXAMPLES 7 AND 8

Except that a mixed powder of Si and Co was used in place of the mixedpower of Fe and Sn in such a manner that a composite particle comprised30 parts by weight of Si as a solid phase A and 70 parts by weight of asolid solution of Co and Si as a solid phase B, and that the time forsynthesis by mechanical alloying was 10 and 15 hours, the respectivenegative electrode materials B6 and B7 were produced on the sameconditions as in Example 1. Subsequently, except that the negativeelectrode materials B6 and B7 were used in place of the negativeelectrode material A2, the respective batteries were produced in thesame manner as in Example 1.

COMPARATIVE EXAMPLE 7 AND 8

Except that the time for synthesis by mechanical alloying was 3 and 20hours, the respective negative electrode materials B5 and B8 wereproduced in the same conditions as in Example 7. Further, except thatthe negative electrode materials B5 and B8 were used in place of thenegative electrode material A2, the respective batteries were producedin the same manner as in Example 1.

EXAMPLES 9 AND 10

Except that a mixed powder of Zn and V was used in place of the mixedpower of Fe and Sn in such a manner that a composite particle comprised10 parts by weight of Zn as a solid phase A and 90 parts by weight ofVZn₁₆ as a solid phase B, and that the time for synthesis by mechanicalalloying was 10 and 15 hours, the respective negative electrodematerials C2 and C3 were produced on the same conditions as inExample 1. Subsequently, except that the negative electrode materials C2and C3 were used in place of the negative electrode material A2, therespective batteries were produced in the same manner as in Example 1.

COMPARATIVE EXAMPLES 9 AND 10

Except that the time for synthesis by mechanical alloying was 3 and 20hours, the respective negative electrode materials C1 and C4 wereproduced in the same conditions as in Example 9. Further, except thatthe negative electrode materials C1 and C4 were used in place of thenegative electrode material A2, the respective batteries were producedin the same manner as in Example 1.

EXAMPLES 11 AND 12

Except that a mixed powder of Zn and V was used in place of the mixedpower of Fe and Sn in such a manner that a composite particle comprised40 parts by weight of Zn as a solid phase A and 60 parts by weight of asolid solution of Zn and Cu as a solid phase B, and that the time forsynthesis by mechanical alloying was 10 and 15 hours, the respectivenegative electrode materials C6 and C7 were produced on the sameconditions as in Example 1. Subsequently, except that the negativeelectrode materials C6 and C7 were used in place of the negativeelectrode material A2, the respective batteries were produced in thesame manner as in Example 1.

COMPARATIVE EXAMPLES 11 AND 12

Except that the time for synthesis by mechanical alloying was 3 and 20hours, the respective negative electrode materials C5 and C8 wereproduced on the same conditions as in Example 11. Further, except thatthe negative electrode materials C5 and C8 were used in place of thenegative electrode material A2, the respective batteries were producedin the same manner as in Example 1.

EXAMPLES 13 AND 14

Except that a mixed powder of Sn and Ti was used in place of the mixedpower of Sn and Fe in such a manner that a composite particle comprised22 parts by weight of Sn as a solid phase A and 78 parts by weight ofTi₂Sn as a solid phase B, and that the time for synthesis by mechanicalalloying was 15 and 10 hours, the respective negative electrodematerials D2 and D3 were produced on the same conditions as inExample 1. Subsequently, except that the negative electrode materials D2and D3 were used in place of the negative electrode material A2, therespective batteries were produced in the same manner as in Example 1.

COMPARATIVE EXAMPLES 13 AND 14

Except that the time for synthesis by mechanical alloying was 20 and 3hours, the respective negative electrode materials D1 and D4 wereproduced on the same conditions as in Example 13. Further, except thatthe negative electrode materials D1 and D4 were used in place of thenegative electrode material A2, the respective batteries were producedin the same manner as in Example 1.

EXAMPLES 15 AND 16

Except that a mixed powder of Sn and Ti was used in place of the mixedpower of Sn and Fe in such a manner that a composite particle comprised26 parts by weight of Sn as a solid phase A and 74 parts by weight of asolid solution of Ti and Sn as a solid phase B, and that the time forsynthesis by mechanical alloying was 15 and 10 hours, the respectivenegative electrode materials D6 and D7 were produced on the sameconditions as in Example 1. Subsequently, except that the negativeelectrode materials D6 and D7 were used in place of the negativeelectrode material A2, the respective batteries were produced in thesame manner as in Example 1.

COMPARATIVE EXAMPLES 15 AND 16

Except that the time for synthesis by mechanical alloying was 20 and 3hours, the respective negative electrode materials D5 and D8 wereproduced on the same conditions as in Example 15. Further, except thatthe negative electrode materials D5 and D8 were used in place of thenegative electrode material A2, the respective batteries were producedin the same manner as in Example 1.

EXAMPLES 17 AND 18

Except that a mixed powder of Si and Ni was used in place of the mixedpower of Sn and Fe in such a manner that a composite particle comprised12 parts by weight of Si as a solid phase A and 88 parts by weight ofNiSi₂ as a solid phase B, and that the time for synthesis by mechanicalalloying was 15 and 10 hours, the respective negative electrodematerials E2 and E3 were produced on the same conditions as inExample 1. Subsequently, except that the negative electrode materials E2and E3 were used in place of the negative electrode material A2, therespective batteries were produced in the same manner as in Example 1.

COMPARATIVE EXAMPLES 17 and 18

Except that the time for synthesis by mechanical alloying was 20 and 3hours, the respective negative electrode materials E1 and E4 wereproduced on the same conditions as in Example 17. Further, except thatthe negative electrode materials E1 and E4 were used in place of thenegative electrode material A2, the respective batteries were producedin the same manner as in Example 1.

EXAMPLES 19 AND 20

Except that a mixed powder of Si and Ni was used in place of the mixedpower of Sn and Fe in such a manner that a composite particle comprised28 parts by weight of Si as a solid phase A and 72 parts by weight of asolid solution of Ni and Si as a solid phase B, and that the time forsynthesis by mechanical alloying was 15 and 10 hours, the respectivenegative electrode materials E6 and E7 were produced on the sameconditions as in Example 1. Subsequently, except that the negativeelectrode materials E6 and E7 were used in place of the negativeelectrode material A2, the respective batteries were produced in thesame manner as in Example 1.

COMPARATIVE EXAMPLES 19 AND 20

Except that the time for synthesis by mechanical alloying was 20 and 3hours, the respective negative electrode materials E5 and E8 wereproduced on the same conditions as in Example 19. Further, except thatthe negative electrode materials E5 and E8 were used in place of thenegative electrode material A2, the respective batteries were producedin the same manner as in Example 1.

EXAMPLES 21 AND 22

Except that a mixed powder of Zn and Mg was used in place of the mixedpower of Sn and Fe in such a manner that a composite particle comprised15 parts by weight of Zn as a solid phase A and 85 parts by weight ofMg₂Zn₁₁ as a solid phase B, and that the time for synthesis bymechanical alloying was 15 and 10 hours, the respective negativeelectrode materials F2 and F3 were produced on the same conditions as inExample 1. Subsequently, except that the negative electrode materials F2and F3 were used in place of the negative electrode material A2, therespective batteries were produced in the same manner as in Example 1.

COMPARATIVE EXAMPLES 21 AND 22

Except that the time for synthesis by mechanical alloying was 20 and 3hours, the respective negative electrode materials F1 and F4 wereproduced in the same conditions as in Example 21. Further, except thatthe negative electrode materials F1 and F4 were used in place of thenegative electrode material A2, the respective batteries were producedin the same manner as in Example 1.

EXAMPLES 23 AND 24

Except that a mixed powder of Cd and Zn was used in place of the mixedpower of Sn and Fe in such a manner that a composite particle comprised35 parts by weight of Zn as a solid phase A and 65 parts by weight of asolid solution of Cd and Zn as a solid phase B, and that the time forsynthesis by mechanical alloying was 15 and 10 hours, the respectivenegative electrode materials F6 and F7 were produced on the sameconditions as in Example 1. Subsequently, except that the negativeelectrode materials F6 and F7 were used in place of the negativeelectrode material A2, the respective batteries were produced in thesame manner as in Example 1.

COMPARATIVE EXAMPLES 23 AND 24

Except that the time for synthesis by mechanical alloying was 20 and 3hours, the respective negative electrode materials F5 and F8 wereproduced in the same conditions as in Example 23. Further, except thatthe negative electrode materials F5 and F8 were used in place of thenegative electrode material A2, the respective batteries were producedin the same manner as in Example 1.

COMPARATIVE EXAMPLE 25

Except that graphite was used for a negative electrode material in placeof the composite particle comprising a solid phase A and a solid phase Bin accordance with the present invention, a negative electrode wasproduced in the same manner as in Example 1. A battery was then producedin the same manner as in Example 1.

EXAMPLE 25

Except that a mixed powder of Si and Cd was used in place of the mixedpower of Sn and Fe in such a manner that a composite particle comprised20 parts by weight of Si as a solid phase A and 80 parts by weight ofCdSi₂ as a solid phase B, a negative electrode material G1 was producedon the same conditions as in Example 1. Subsequently, except that thenegative electrode material G1 was used in place of the negativeelectrode material A2, a battery was produced in the same manner as inExample 1.

EXAMPLE 26

Except that a mixed powder of Si and Ni was used in place of the mixedpower of Sn and Fe in such a manner that a composite particle comprised20 parts by weight of Si as a solid phase A and 80 parts by weight ofNiSi₂ as a solid phase B, a negative electrode material G2 was producedon the same conditions as in Example 1. Subsequently, except that thenegative electrode material G2 was used in place of the negativeelectrode material A2, a battery was produced in the same manner as inExample 1.

EXAMPLE 27

Except that a mixed powder of Si and W was used in place of the mixedpower of Sn and Fe in such a manner that a composite particle comprised20 parts by weight of Si as a solid phase A and 80 parts by weight ofWSi₂ as a solid phase B, a negative electrode material G3 was producedon the same conditions as in Example 1. Subsequently, except that thenegative electrode material G3 was used in place of the negativeelectrode material A2, a battery was produced in the same manner as inExample 1.

EXAMPLE 28

Except that a mixed powder of Si and Cu was used in place of the mixedpower of Sn and Fe in such a manner that a composite particle comprised20 parts by weight of Si as a solid phase A and 80 parts by weight ofCuSi₂ as a solid phase B, a negative electrode material G4 was producedon the same conditions as in Example 1. Subsequently, except that thenegative electrode material G4 was used in place of the negativeelectrode material A2, a battery was produced in the same manner as inExample 1.

EXAMPLE 29

Except that a mixed powder of Ti and Si was used in place of the mixedpower of Sn and Fe in such a manner that a composite particle comprised20 parts by weight of Si as a solid phase A and 80 parts by weight ofTiSi₂ having the crystal structure of Fddd as a solid phase B, anegative electrode material G5 was produced on the same conditions as inExample 1. Subsequently, except that the negative electrode material G5was used in place of the negative electrode material A2, a battery wasproduced in the same manner as in Example 1.

EXAMPLE 30

Except that a mixed powder of Ti and Si was used in place of the mixedpower of Sn and Fe in such a manner that a composite particle comprised20 parts by weight of Si as a solid phase A and 80 parts by weight ofTiSi₂ having the crystal structure of Cmcm as a solid phase B, anegative electrode material G6 was produced on the same conditions as inExample 1. Subsequently, except that the negative electrode material G6was used in place of the negative electrode material A2, a battery wasproduced in the same manner as in Example 1.

EXAMPLE 31

Except that a mixed powder of Ti and Si was used in place of the mixedpower of Sn and Fe in such a manner that a composite particle comprised20 parts by weight of Si as a solid phase A and 80 parts by weight ofTiSi₂, having the crystal structure of Fddd and Cmcm which arecoexistent, as a solid phase B, a negative electrode material G7 wasproduced on the same conditions as in Example 1. Subsequently, exceptthat the negative electrode material G7 was used in place of thenegative electrode material A2, a battery was produced in the samemanner as in Example 1.

[Evaluation of Negative Electrode Material and Battery]

(1) Wide-Angle X-Ray Diffraction Measurement

Wide-angle X-ray diffraction measurements of the respective negativeelectrode materials A1 to A8, B1 to B8, C1 to C8, D1 to D8, E1 to E8, F1to F8 and G1 to G7 of Examples 1 to 31 and Comparative Examples 1 to 24were made.

RINT-2500 (manufactured by Rigaku International Corporation) was used inthe wide-angel X-ray diffraction measurements with CuKa used as a sourceof X-rays. Using a measurement method (Hand book on Diffraction ofX-rays (Fourth Revised Edition), Rigaku International Corporation, page42) in which a sample is made to have no orientation, fine particleswere filled in a sample holder to be measured. As the sample to bemeasured, fine particles before production of a negative electrode maybe used, or one obtained by collecting an electrode material mixtureafter production of a negative electrode and then sufficientlyseparating the particles in a mortar may be used. Further, whendiffraction of wide-angle X-rays was measured, a sample surface on whichX-rays were incident was made flat. This surface was aligned with arotation axis of a goniometer so as to prevent occurrence of an error inmeasuring diffraction angles and intensity. By the wide-angel X-raydiffraction measurement, the maximum diffracted X-ray intensity (I_(A))attributed to the solid phase A and the maximum diffracted X-rayintensity (I_(B)) attributed to the solid phase B were measured and thenthe ratio (I_(A)/I_(B)) of the maximum diffracted X-ray intensities wascalculated.

The diffracted X-ray intensity may be represented using either peakintensity which is shown by a profile of a diffraction line obtained bythe wide-angel X-ray diffraction measurement, or integrated intensitywhich is obtained from a profile of a diffraction line or counting data,and there is almost no substantial difference therebetween. Moreover,the profile of the diffraction line at this time may either include orexclude background intensity.

Further, in each of Examples 29 to 31, even when the peak of TiSi₂attributed to the crystal structure of Cmcm or Fddd as obtained by thewide-angle X-ray diffraction measurement was shifted to the high angleside or the low angle side, this was regarded as the peak of thediffraction of TiSi₂, attributed to the crystal structure of Cmcm orFddd.

(2) Charge/Discharge Cycle Test

A charge/discharge cycle test was conducted on the respective batteriesusing the negative electrode materials A1 to A8, B1 to B8, C1 to C8, D1to D8, E1 to E8, F1 to F8 and G1 to G7 of Examples 1 to 31 andComparative Examples 1 to 24, and graphite of Comparative Example 25.

In a charge/discharge cycle, it is repeated to charge a battery at aconstant current of 1000 mA until a voltage reached 4.2 V and todischarge the battery at a constant current of 1000 mA until the voltagedropped to 2.0 V in a constant temperature container at 20%. Thischarge/discharge cycle was repeated 100 times and a capacity maintenanceratio at the 100th cycle was measured. It is to be noted that thecapacity maintenance ratio was represented by a relative value of adischarge capacity at the 100th cycle to an initial discharge capacitywhich was assumed as 100.

Table 1 showed I_(A)/I_(B) values obtained by the wide-angle X-raydiffraction measurements of the respective negative electrode materialsof Examples 1 to 12 and Comparative Examples of 1 to 12, and the initialcapacities as well as capacity maintenance ratios of the respectivebatteries using, for the negative electrodes thereof, the aforesaidnegative electrode materials and graphite of Comparative Example 25.TABLE 1 Initial Capacity Negative discharge maintenance electrode SolidSolid capacity ratio material phase A phase B I_(A)/I_(B) (mAh) (%) A1Sn FeSn₂ 0.2 2200 50 A2 Sn FeSn₂ 0.1 2255 90 A3 Sn FeSn₂ 0.001 2240 91A4 Sn FeSn₂ 0.0005 1600 75 A5 Sn Fe,Sn 0.3 2295 45 Solid solution A6 SnFe,Sn 0.1 2230 91 Solid solution A7 Sn Fe,Sn 0.001 2210 92 Solidsolution A8 Sn Fe,Sn 0.0005 1580 78 Solid solution B1 Si CoSi₂ 0.2 230051 B2 Si CoSi₂ 0.1 2355 91 B3 Si CoSi₂ 0.001 2340 90 B4 Si CoSi₂ 0.00051600 76 B5 Si Si,Co 0.3 2395 46 Solid solution B6 Si Si,Co 0.1 2330 92Solid solution B7 Si Si,Co 0.001 2310 91 Solid solution B8 Si Si,Co0.0005 1580 78 Solid solution C1 Zn VZn₁₆ 0.2 2100 51 C2 Zn VZn₁₆ 0.12155 91 C3 Zn VZn₁₆ 0.001 2140 90 C4 Zn VZn₁₆ 0.0005 1600 76 C5 Zn Zn,Cu0.3 2195 46 Solid solution C6 Zn Zn,Cu 0.1 2130 90 Solid solution C7 ZnZn,Cu 0.001 2110 91 Solid solution C8 Zn Zn,Cu 0.0005 1580 78 Solidsolution Graphite — — — 1800 89

As for the negative electrode materials A1 to A8, in both the case ofthe negative electrode materials A1 to A4 with the solid phase Bcomprising the intermetallic compound FeSn₂ and the case of the negativeelectrode materials A5 to A8 with the solid phase B comprising a solidsolution of Fe and Sn, when I_(A)/I_(B) was not less than 0.001, thedischarge capacity was not lower than 2200 mAh, which was higher thanthat in Comparative Example 25 where graphite was used as the negativeelectrode material. Further, when I_(A)/I_(B) was 0.1 or less, thecapacity maintenance ratio was not lower than 90%, which was higher thanthat in Comparative Example 25 where graphite was used as the negativeelectrode material. It was therefore possible to obtain a high capacityas well as a high capacity maintenance ratio when I_(A)/I_(B) was in therange represented by 0.001≦I_(A)/I_(B)≦0.1, as in the case of using thenegative electrode materials A2, A3, A6 and A7 in Examples 1 to 4.

As for the negative electrode materials B1 to B8, in both the case ofthe negative electrode materials B1 to B4 with the solid phase Bcomprising the intermetallic compound CoSi₂ and the case of the negativeelectrode materials B5 to B8 with the solid phase B comprising a solidsolution of Si and Co, when I_(A)/I_(B) was not less than 0.001, thedischarge capacity was not lower than 2300 mAh, which was higher thanthat in Comparative Example 25 where graphite was used as the negativeelectrode material. Further, when I_(A)/I_(B) was 0.1 or less, thecapacity maintenance ratio was not lower than 90%, which was higher thanthat in Comparative Example 25 where graphite was used as the negativeelectrode material. It was therefore possible to obtain a high capacityas well as a high capacity maintenance ratio when I_(A)/I_(B) was in therange represented by 0.001≦I_(A)/I_(B)≦0.1, as in the case of using thenegative electrode materials B2, B3, B6 and B7 in Examples 5 to 8.

As for the negative electrode materials C1 to C8, in both the case ofthe negative electrode materials C1 to C4 with the solid phase Bcomprising the intermetallic compound VZn₁₆ and the case of the negativeelectrode materials C5 to C8 with the solid phase B comprising a solidsolution of Zn and Cu, when I_(A)/I_(B) was not less than 0.001, thedischarge capacity was not lower than 2100 mAh, which was higher thanthat in Comparative Example 25 where graphite was used as the negativeelectrode material. Further, when I_(A)/I_(B) was 0.1 or less, thecapacity maintenance ratio was not lower than 90%, which was higher thanthat in Comparative Example 25 where graphite was used as the negativeelectrode material. It was therefore possible to obtain a high capacityas well as a high capacity maintenance ratio when I_(A)/I_(B) was in therange represented by 0.001≦I_(A)/I_(B)≦0.1, as in the case of using thenegative electrode materials C2, C3, C6 and C7 in Examples 9 to 12.

Table 2 showed W values obtained by the wide-angle X-ray diffractionmeasurements of the respective negative electrode materials of Examples13 to 24 and Comparative Examples 13 to 24, and initial capacities aswell as capacities maintenance ratios of the respective batteries usingnegative electrode plates comprising these negative electrode materialsand graphite of Comparative Example 25. TABLE 2 Initial CapacityNegative discharge maintenance electrode Solid Solid W capacity ratiomaterial phase A phase B (rad) (mAh) (%) D1 Sn Ti₂Sn 0.2 2200 50 D2 SnTi₂Sn 0.1 2255 90 D3 Sn Ti₂Sn 0.001 2240 91 D4 Sn Ti₂Sn 0.0005 1600 75D5 Sn Ti,Sn 0.3 2295 45 Solid solution D6 Sn Ti,Sn 0.1 2230 91 Solidsolution D7 Sn Ti,Sn 0.001 2210 92 Solid solution D8 Sn Ti,Sn 0.00051580 73 Solid solution E1 Si NiSi₂ 0.2 2300 51 E2 Si NiSi₂ 0.1 2355 91E3 Si NiSi₂ 0.001 2340 90 E4 Si NiSi₂ 0.0005 1600 75 E5 Si Si,Ni 0.32395 46 Solid solution E6 Si Si,Ni 0.1 2330 90 Solid solution E7 SiSi,Ni 0.001 2310 91 Solid solution E8 Si Si,Ni 0.0005 1580 72 Solidsolution F1 Zn Mg₂Zn₁₁ 0.2 2300 50 F2 Zn Mg₂Zn₁₁ 0.1 2355 90 F3 ZnMg₂Zn₁₁ 0.001 2340 90 F4 Zn Mg₂Zn₁₁ 0.0005 1600 69 F5 Zn Zn,Cd 0.3 239547 Solid solution F6 Zn Zn,Cd 0.1 2330 91 Solid solution F7 Zn Zn,Cd0.001 2310 92 Solid solution F8 Zn Zn,Cd 0.0005 1580 63 Solid solutionGraphite — — — 1800 89

As for the negative electrode materials D1 to D8, in both the case ofthe negative electrode materials D1 to D4 with the solid phase Bcomprising the intermetallic compound Ti₂Sn and the case of the negativeelectrode materials D5 to D8 with the solid phase B comprising a solidsolution of Ti and Sn, when W was not smaller than 0.001 radian, thedischarge capacity was not lower than 2200 mAh, which was higher thanthat in Comparative Example 25 where graphite was used as the negativeelectrode material. Further, when W (radian) was in the rangerepresented by 0.001≦W≦0.1, the capacity maintenance ratio was not lowerthan 90%, which was higher than that in Comparative Example 25 wheregraphite was used as the negative electrode material. It was thereforepossible to obtain a high capacity as well as a high capacitymaintenance ratio when W (radian) was in the range represented by0.001≦W≦0.1, as in the case of using the negative electrode materialsD2, D3, D6 and D7 in Examples 13 to 16.

As for the negative electrode materials E1 to E8, in both the case ofthe negative electrode materials E1 to E4 with the solid phase Bcomprising the inteinmetallic compound NiSi₂ and the case of thenegative electrode materials E5 to E8 with the solid phase B comprisinga solid solution of Si and Ni, when W was not smaller than 0.001 radian,the discharge capacity was not lower than 2300 mAh, which was higherthan that in Comparative Example 25 where graphite was used as thenegative electrode material. Further, when W (radian) was in the rangerepresented by 0.001≦W≦0.1, the capacity maintenance ratio was not lowerthan 90%, which was higher than that in Comparative Example 25 wheregraphite was used as the negative electrode material. It was thereforepossible to obtain a high capacity as well as a high capacitymaintenance ratio when W (radian) was in the range represented by0.001≦W≦0.1, as in the case of using the negative electrode materialsE2, E3, E6 and E7 in Examples 17 to 20.

As for the negative electrode materials F1 to F8, in both the case ofthe negative electrode materials F1 to F4 with the solid phase Bcomprising the intermetallic compound Mg₂Zn₁₁ and the case of thenegative electrode materials F5 to F8 with the solid phase B comprisinga solid solution of Zn and Cd, when W was not smaller than 0.001 radian,the discharge capacity was not lower than 2100 mAh, which was higherthan that in Comparative Example 25 where graphite was used as thenegative electrode material. Further, when W (radian) was in the rangerepresented by 0.001% W≦0.1, the capacity maintenance ratio was notlower than 90%, which was higher than that in Comparative Example 25where graphite was used as the negative electrode material. It wastherefore possible to obtain a high capacity as well as a high capacitymaintenance ratio when W (radian) was in the range represented by0.001≦W≦0.1, as in the case of using the negative electrode materialsF2, F3, F6 and F7 in Examples 21 to 24.

Table 3 showed the I_(A)/I_(B) values and W values, obtained by thewide-angle X-ray diffraction measurements of the respective electrodematerials of Examples 25 to 31, and initial capacities as well ascapacities maintenance ratios of the respective batteries using, for thenegative electrodes thereof, the aforesaid negative electrode materialsand graphite of Comparative Example 25. TABLE 3 Negative Initialdischarge Capacity electrode Solid W capacity maintenance ratio materialphase A Solid phase B I_(A)/I_(B) (rad) (mAh) (%) G1 Si CoSi₂ 0.08 0.022350 90 G2 Si NiSi₂ 0.05 0.01 2355 91 G3 Si WSi₂ 0.08 0.03 2340 90 G4 SiCuSi₂ 0.05 0.02 2315 91 G5 Si TiSi₂ (Fddd) 0.08 0.05 2500 92 G6 Si TiSi₂(Cmcm) 0.08 0.05 2510 92 G7 Si TiSi₂ 0.08 0.05 2505 92 (Cmcm/Fdddcoexist) Graphite — — — — 1800 89

In any of the respective batteries using, for the negative electrodesthereof, the materials G1 to G7 with the solid phase A comprising Si,the solid phase B comprising various intermetallic compounds as shown inTable 3, I_(A)/I_(B) being in the range represented by 0.001%I_(A)/I_(B)≦0.1 and W (radian) being in the range represented by 0.001%W≦0.1, the discharge capacity was not lower than 2300 mAh and thecapacity maintenance ratio was not lower than 90%. Especially in thecase of using the materials G5 to G7 where the solid phase B comprisedTiSi₂ having a crystal structure of Cmcm, Fddd, or mixed-state Cmcm andFddd, the discharge capacity was as high as not lower than 2500 mAhwhile the capacity maintenance ratio was as high as 92%.

Revealed therefore was that, in order to obtain a higher capacity aswell as a higher capacity maintenance ratio, it is preferable to use anegative electrode material which comprises a solid phase A comprisingSi, and a solid phase B comprising Ti and Si, and TiSi₂ having a crystalstructure of at least one selected from the group consisting of Cmcm andFddd.

EXAMPLES 32 AND 33

Except that a mixed powder of CuSi₂, Cu₆Sn₅, Si and Sn was used in placeof the mixed power of Sn and Fe in such a manner that a compositeparticle comprised 20 parts by weight of Si and Sn (mole ratio 1:2) as asolid phase A and 80 parts by weight of CuSi₂ and Cu₆Sn₅ (mole ratio1:6) as a solid phase B, and that the time for synthesis by mechanicalalloying was 14 and 12 hours, the respective negative electrodematerials I2 and I3 were produced in the same conditions as inExample 1. Subsequently, except that the negative electrode materials I2and I3 were used in place of the negative electrode material A2, therespective batteries were produced in the same manner as in Example 1.

COMPARATIVE EXAMPLES 26 and 27

Except that the time for synthesis by mechanical alloying was 15 and 11hours, the respective negative electrode materials I1 and I4 wereproduced in the same conditions as in Example 32. Further, except thatthe negative electrode materials I1 and I4 were used in place of thenegative electrode material A2, the respective batteries were producedin the same manner as in Example 1.

EXAMPLES 34 AND 35

Except that a mixed powder of a solid solution of Cu and Si, a solidsolution of Cu and Sn, Si and Sn was used in place of the mixed power ofSn and Fe in such a manner that a composite particle comprised 20 partsby weight of Si and Sn (mole ratio 1:2) as a solid phase A and 80 partsby weight of a solid solution of Cu and Si and a solid solution of Cuand Sn (mole ratio 1:6) as a solid phase B, and that the time forsynthesis by mechanical alloying was 14 and 12 hours, the respectivenegative electrode materials I6 and I7 were produced on the sameconditions as in Example 1. Subsequently, except that the negativeelectrode materials I6 and I7 were used in place of the negativeelectrode material A2, the respective batteries were produced in thesame manner as in Example 1.

Comparative Examples 28 and 29

Except that the time for synthesis by mechanical alloying was 15 and 11hours, the respective negative electrode materials I5 and I8 wereproduced in the same conditions as in Example 34. Further, except thatthe negative electrode materials I5 and I8 were used in place of thenegative electrode material A2, the respective batteries were producedin the same manner as in Example 1.

EXAMPLES 36 AND 37

Except that a mixed powder of CuSi₂, a solid solution of Cu and Sn, Siand Sn was used in place of the mixed power of Sn and Fe in such amanner that a composite particle comprised 20 parts by weight of Si andSn (mole ratio 1:2) as a solid phase A and 80 parts by weight of CuSi₂and a solid solution of Cu and Sn (mole ratio 1:6) as a solid phase B,and that the time for synthesis by mechanical alloying was 14 and 12hours, the respective negative electrode materials I10 and I11 wereproduced on the same conditions as in Example 1. Subsequently, exceptthat the negative electrode materials I10 and I11 were used in place ofthe negative electrode material A2, the respective batteries wereproduced in the same manner as in Example 1.

COMPARATIVE EXAMPLES 30 and 31

Except that the time for synthesis by mechanical alloying was 15 and 11hours, the respective negative electrode materials I9 and I12 wereproduced in the same conditions as in Example 36. Further, except thatthe negative electrode materials I9 and I12 were used in place of thenegative electrode material A2, the respective batteries were producedin the same manner as in Example 1.

EXAMPLES 38 AND 39

Except that a mixed powder of Cu₆Sn₅, a solid solution of Cu and Si, Siand Sn was used in place of the mixed power of Sn and Fe in such amanner that a composite particle comprised 20 parts by weight of Si andSn (mole ratio 1:2) as a solid phase A and 80 parts by weight of Cu₆Sn₅and a solid solution of Cu and Si (mole ratio 1:6) as a solid phase B,and that the time for synthesis by mechanical alloying was 14 and 12hours, the respective negative electrode materials I14 and I15 wereproduced on the same conditions as in Example 1. Subsequently, exceptthat the negative electrode materials I14 and I15 were used in place ofthe negative electrode material A2, the respective batteries wereproduced in the same manner as in Example 1.

COMPARATIVE EXAMPLES 32 and 33

Except that the time for synthesis by mechanical alloying was 15 and 11hours, the respective negative electrode materials I13 and I16 wereproduced in the same conditions as in Example 38. Further, except thatthe negative electrode materials I13 and I16 were used in place of thenegative electrode material A2, the respective batteries were producedin the same manner as in Example 1.

It is to be noted that the solid solution of Cu and Si or the solidsolution of Cu and Sn, used in each of Examples 34 to 39 and ComparativeExamples 28 to 33 above, was one with an atomic ratio of Cu:Si or Cu:Snof 99:1.

Wide-angle X-ray diffraction measurements of the aforesaid respectivenegative electrode materials I1 to I16 of Examples 32 to 39 andComparative Examples 26 to 33 were made in the same manner as in Example1, to obtain W values.

Further, except that the negative electrode materials I1 to I16 wereused in place of the negative electrode material A2, the respectivebatteries were produced in the same manner as in Example 1. Thesebatteries were subjected to the charge/discharge cycle test in the samemanner as in Example 1.

The evaluation results of these batteries were shown in Table 4. TABLE 4Initial Capacity Negative discharge maintenance electrode Solid Solid Wcapacity ratio material phase A phase B (rad) (mAh) (%) I1 Si, Sn CuSi₂,Cu₆Sn₅ 0.2 2280 53 I2 Si, Sn CuSi₂, Cu₆Sn₅ 0.1 2290 91 I3 Si, Sn CuSi₂,Cu₆Sn₅ 0.001 2230 90 I4 Si, Sn CuSi₂, Cu₆Sn₅ 0.0005 2310 73 I5 Si, Sn Cu& Si S/S, 0.2 2279 53 Cu & Sn S/S I6 Si, Sn Cu & Si S/S, 0.1 2289 91 Cu& Sn S/S I7 Si, Sn Cu & Si S/S, 0.001 2229 90 Cu & Sn S/S I8 Si, Sn Cu &Si S/S, 0.0005 2309 73 Cu & Sn S/S I9 Si, Sn CuSi₂, 0.2 2281 53 Cu & SnS/S I10  Si, Sn CuSi₂, 0.1 2291 91 Cu & Sn S/S I11  Si, Sn CuSi₂, 0.0012231 90 Cu & Sn S/S I12  Si, Sn CuSi₂, 0.0005 2311 73 Cu & Sn S/S I13 Si, Sn Cu & Si S/S, 0.2 2282 53 Cu₆Sn₅ I14  Si, Sn Cu & Si S/S, 0.1 229291 Cu₆Sn₅ I15  Si, Sn Cu & Si S/S, 0.001 2232 90 Cu₆Sn₅ I16  Si, Sn Cu &Si S/S, 0.0005 2312 73 Cu₆Sn₅S/S: Solid solution

It was revealed that each of the capacity maintenance ratios wasdependent on the W value while all the initial discharge capacities werenot lower than 2200 mAh, as indicated in Table 4. More specifically, itwas found that when the W value was 0.001≦W≦0.1, the capacitymaintenance ratio was a favorable value of about 90 to 91%.

As thus described, a high capacity and a high capacity maintenance ratiowere obtained with a composite particle used as the negative electrodematerial, including a solid phase A comprising Si and Sn, a solid phaseB comprising a solid solution or an intermetallic compound, whichcontained Cu, Si and Sn, and a W value satisfied 0.001≦W≦0.1.

EXAMPLES 40 AND 41

Except that a mixed powder of CuSi₂, Cu₆Sn₅, Si and Sn was used in placeof the mixed power of Sn and Fe in such a manner that a compositeparticle comprised 20 parts by weight of Si and Sn (mole ratio 1:3) as asolid phase A and 80 parts by weight of CuSi₂ and Cu₆Sn₅ (mole ratio1:6) as a solid phase B, and that the time for synthesis by mechanicalalloying was 14 and 12 hours, the respective negative electrodematerials I18 and I19 were produced on the same conditions as inExample 1. Subsequently, except that the negative electrode materialsI18 and I19 were used in place of the negative electrode material A2,the respective batteries were produced in the same manner as in Example1.

COMPARATIVE EXAMPLES 34 and 35

Except that the time for synthesis by mechanical alloying was 15 and 11hours, the respective negative electrode materials I17 and I20 wereproduced in the same conditions as in Example 40. Further, except thatthe negative electrode materials I17 and I20 were used in place of thenegative electrode material A2, the respective batteries were producedin the same manner as in Example 1.

EXAMPLES 42 AND 43

Except that a mixed powder of a solid solution of Cu and Si, a solidsolution of Cu and Sn, Si and Sn was used in place of the mixed power ofSn and Fe in such a manner that a composite particle comprised 20 partsby weight of Si and Sn (mole ratio 1:3) as a solid phase A and 80 partsby weight of a solid solution of Cu and Si and a solid solution of Cuand Sn (mole ratio 1:6) as a solid phase B, and that the time forsynthesis by mechanical alloying was 14 and 12 hours, the respectivenegative electrode materials I22 and I23 were produced on the sameconditions as in Example 1. Subsequently, except that the negativeelectrode materials I22 and I23 were used in place of the negativeelectrode material A2, the respective batteries were produced in thesame manner as in Example 1.

COMPARATIVE EXAMPLES 36 AND 37

Except that the time for synthesis by mechanical alloying was 15 and 11hours, the respective negative electrode materials I21 and I24 wereproduced in the same conditions as in Example 42. Further, except thatthe negative electrode materials I21 and I24 were used in place of thenegative electrode material A2, the respective batteries were producedin the same manner as in Example 1.

EXAMPLES 44 AND 45

Except that a mixed powder of CuSi₂, a solid solution of Cu and Sn, Siand Sn was used in place of the mixed power of Sn and Fe in such amanner that a composite particle comprised 20 parts by weight of Si andSn (mole ratio 1:3) as a solid phase A and 80 parts by weight of CuSi₂and a solid solution of Cu and Sn (mole ratio 1:6), the time forsynthesis by mechanical alloying was 14 and 12 hours, the respectivenegative electrode materials I26 and I27 were produced on the sameconditions as in Example 1. Subsequently, except that the negativeelectrode materials I26 and I27 were used in place of the negativeelectrode material A2, the respective batteries were produced in thesame manner as in Example 1.

Comparative Examples 38 and 39

Except that the time for synthesis by mechanical alloying was 15 and 11hours, the respective negative electrode materials I25 and I28 wereproduced in the same conditions as in Example 44. Further, except thatthe negative electrode materials I25 and I28 were used in place of thenegative electrode material A2, the respective batteries were producedin the same manner as in Example 1.

EXAMPLES 46 AND 47

Except that a mixed powder of Cu₆Sn₅, a solid solution of Cu and Si, Siand Sn was used in place of the mixed power of Sn and Fe in such amanner that a composite particle comprised 20 parts by weight of Si andSn (mole ratio 1:3) as a solid phase A and 80 parts by weight of a solidsolution of Cu and Si, and Cu₆Sn₅ (mole ratio 1:6), and that the timefor synthesis by mechanical alloying was 14 and 12 hours, the respectivenegative electrode materials I30 and I31 were produced on the sameconditions as in Example 1. Subsequently, except that the negativeelectrode materials I30 and I31 were used in place of the negativeelectrode material A2, the respective batteries were produced in thesame manner as in Example 1.

COMPARATIVE EXAMPLES 40 AND 41

Except that the time for synthesis by mechanical alloying was 15 and 11hours, the respective negative electrode materials I29 and I32 wereproduced in the same conditions as in Example 46. Further, except thatthe negative electrode materials I29 and I32 were used in place of thenegative electrode material A2, the respective batteries were producedin the same manner as in Example 1.

It is to be noted that the solid solution of Cu and Si or the solidsolution of Cu and Sn, used in each of Examples 42 to 47 and ComparativeExamples 36 to 41 above, was one with an atomic ratio of Cu:Si or Cu:Snof 99:1.

The wide-angle X-ray diffraction measurements of the aforesaidrespective negative electrode materials I17 to 32 of Examples 40 to 47and Comparative Examples 34 to 41 were made in the same manner as inExample 1, to obtain I_(A)/I_(B) values.

Further, except that the negative electrode materials I17 to I32 wereused in place of the negative electrode material A2, the respectivebatteries were produced in the same manner as in Example 1. Thesebatteries were subjected to the charge/discharge cycle test in the samemanner as in Example 1.

The evaluation results of these batteries were shown in Table 5. TABLE 5Initial Capacity Negative discharge maintenance electrode Solid Solidcapacity ratio material phase A phase B I_(A)/I_(B) (mAh) (%) I17 Si, SnCuSi₂, Cu₆Sn₅ 0.0008 2240 52 I18 Si, Sn CuSi₂, Cu₆Sn₅ 0.001 2250 91 I19Si, Sn CuSi₂, Cu₆Sn₅ 0.1 2210 90 I20 Si, Sn CuSi₂, Cu₆Sn₅ 0.3 2286 72I21 Si, Sn Cu & Si S/S, 0.0008 2255 51 Cu & Sn S/S I22 Si, Sn Cu & SiS/S, 0.001 2288 91 Cu & Sn S/S I23 Si, Sn Cu & Si S/S, 0.1 2231 90 Cu &Sn S/S I24 Si, Sn Cu & Si S/S, 0.3 2299 70 Cu & Sn S/S I25 Si, Sn CuSi₂,0.0008 2279 50 Cu & Sn S/S I26 Si, Sn CuSi₂, 0.001 2288 91 Cu & Sn S/SI27 Si, Sn CuSi₂, 0.1 2223 90 Cu & Sn S/S I28 Si, Sn CuSi₂, 0.3 2302 74Cu & Sn S/S I29 Si, Sn Cu & Si S/S, 0.0008 2262 54 Cu₆Sn₅ I30 Si, Sn Cu& Si S/S, 0.001 2282 91 Cu₆Sn₅ I31 Si, Sn Cu & Si S/S, 0.1 2233 90Cu₆Sn₅ I32 Si, Sn Cu & Si S/S, 0.3 2305 71 Cu₆Sn₅S/S: Solid solution

It was revealed that each of the capacity maintenance ratios wasdependent on the I_(A)/I_(B) value while all the initial dischargecapacities were not lower than 2200 mAh, as indicated in Table 5. Morespecifically, it was found that when the I_(A)/I_(B) value was0.001≦I_(A)/I_(B)≦0.1, the capacity maintenance ratio was a favorablevalue of about 90 to 91%.

As thus described, a high capacity and a high capacity maintenance ratiowere obtained with a composite particle used as the negative electrodematerial, including a solid phase A comprising Si and Sn, a solid phaseB comprising a solid solution or an intermetallic compound, whichcontained Cu, Si and Sn, and an I_(A)/I_(B) value satisfied0.001≦I_(A)/I_(B)≦0.1.

EXAMPLES 48 TO 55 AND COMPARATIVE EXAMPLES 42 AND 43

Except that a mixed powder of Ti and Si was used in place of the mixedpower of Sn and Fe in such a manner that a composite particle comprised20 parts by weight of Si as a solid phase A and 80 parts by weight ofTiSi₂ as a solid phase B, and that the time for synthesis by mechanicalalloying was as shown in Table 6, the respective negative electrodematerials H2 to H9 of Examples 48 to 55 and the respective negativeelectrode materials H1 and H10 of Comparative Examples 42 and 43 wereproduced on the same conditions as in Example 1.

Wide-angle X-ray diffraction measurements of the aforesaid respectivenegative electrode materials H1 to H10 were made in the same manner asin Example 1, to obtain W values.

Further, except that the negative electrode materials H1 to H10 wereused in place of the negative electrode material A2, the respectivebatteries were produced in the same manner as in Example 1. Thesebatteries were subjected to the charge/discharge cycle test in the samemanner as in Example 1.

The evaluation results of these batteries were shown in Table 6. TABLE 6Capacity Initial mainten- Negative Solid Synthesis discharge anceelectrode Solid phase time W capacity ratio material phase A B (hr)(rad) (mAh) (%) H1 Si TiSi₂ 10.1 0.0008 2519 65 H2 Si TiSi₂ 10.5 0.0012521 90 H3 Si TiSi₂ 11.0 0.005 2520 92 H4 Si TiSi₂ 11.5 0.008 2530 93 H5Si TiSi₂ 12.0 0.01 2525 93 H6 Si TiSi₂ 12.5 0.02 2535 93 H7 Si TiSi₂13.0 0.04 2532 93 H8 Si TiSi₂ 13.5 0.06 2528 92 H9 Si TiSi₂ 14.0 0.12522 90 H10  Si TiSi₂ 14.5 0.2 2518 60

A high capacity and a high capacity maintenance ratio were obtained witha composite particle used as the negative electrode material, includinga solid phase A comprising Si, a solid phase B comprising TiSi₂, and theW value satisfying 0.001≦W≦0.1. It was also found that a compositeparticle whose W value satisfying 0.008≦W≦0.04 was particularlypreferred since the capacity maintenance ratio then became as high as93%.

It should be noted that there can be obtained a similar effect when thesolid phase B in the negative electrode material of the presentinvention comprises, as the other element than the constituent elementof the solid phase A, an element selected from the elements of Group 2,transition, Group 12 and Group 13 and the Group 14 element excludingcarbon, which are different from the elements used in the presentexamples.

Further, there is no particular limitation on the nominal ratio of theconstituent elements in the negative electrode material; the negativeelectrode material may comprise two phases in such a state that the onephase (solid phase A) which is mainly composed of Sn, Si and Zn isdispersed in the other phase (solid phase B), and this does notparticularly limit the nominal composition.

Moreover, the solid phase A may comprise, in addition to Sn, Si or Zn, asmall amount of an element selected from O, C, N, S, Ca, Mg, Al, Fe, W,V, Ti, Cu, Cr, Co and P, for example.

The solid phase B may comprise, in addition to the solid solution or theintermetallic compound as indicated in the present examples, a smallamount of an element selected from O, C, N, S, Ca, Mg, Al, Fe, W, V, Ti,Cu, Cr, Co and P, for example.

INDUSTRIAL APPLICABILITY

As thus described, according to the present invention, it is possible toprovide a negative electrode material capable of suppressingpulverization thereof due to repeated cycles. It is also possible by theuse of this negative electrode material to provide a non-aqueouselectrolyte secondary battery with a high capacity and an excellentcycle life characteristic.

1. A negative electrode material for non-aqueous electrolyte secondary batteries, which is capable of absorbing and desorbing lithium, characterized in that said negative electrode material comprises a composite particle including solid phases A and B, said solid phase A being dispersed in said solid phase B, said solid phase A comprises at least one element selected from the group consisting of silicon, tin and zinc, said solid phase B comprises a solid solution or an intermetallic compound, which contains: the constituent element of said solid phase A; and at least one element selected from the group consisting of the elements of Group 2, transition, Group 12, Group 13 and Group 14 which are listed in Long Form of Periodic Table, except for the constituent element of said solid phase A and carbon, and the ratio (I_(A)/I_(B)) of the maximum diffracted X-ray intensity (I_(A)) attributed to said solid phase A to the maximum diffracted X-ray intensity (I_(B)) attributed to said solid phase B satisfies 0.001≦I_(A)/I_(B)≦0.1, in terms of a diffraction line obtained by a wide-angle X-ray diffraction measurement of said composite particle.
 2. A negative electrode material for non-aqueous electrolyte secondary batteries, which is capable of absorbing and desorbing lithium, characterized in that said negative electrode material comprises a composite particle including solid phases A and B, said solid phase A being dispersed in said solid phase B, said solid phase A comprises at least one element selected from the group consisting of silicon, tin and zinc, said solid phase B comprises a solid solution or an intermetallic compound, which contains: the constituent element of said solid phase A; and at least one element selected from the group consisting of the elements of Group 2, transition, Group 12, Group 13 and Group 14 which are listed in Long Form of Periodic Table, except for the constituent element of said solid phase A and carbon, and the half width (W) (radian) of the maximum peak intensity of diffracted X-rays, attributed to said solid phase A, satisfies 0.001≦W≦0.1, in terms of a diffraction line obtained by a wide-angle X-ray diffraction measurement of said composite particle.
 3. The negative electrode material for non-aqueous electrolyte secondary batteries in accordance with claim 1 or 2, wherein said solid phase A comprises Si and Sn, and said solid phase B comprises a solid solution or an intermetallic compound, which contains Cu and at least one of Sn and Si.
 4. The negative electrode material for non-aqueous electrolyte secondary batteries in accordance with claim 3, wherein said solid phase B comprises CuSi₂ and Cu₆Sn₅.
 5. The negative electrode material for non-aqueous electrolyte secondary batteries in accordance with claim 3, wherein said solid phase B comprises CuSi₂ and a solid solution containing Cu and Sn.
 6. The negative electrode material for non-aqueous electrolyte secondary batteries in accordance with claim 3, wherein said solid phase B comprises Cu₆Sn₅ and a solid solution containing Cu and Si.
 7. The negative electrode material for non-aqueous electrolyte secondary batteries in accordance with claim 3, wherein said solid phase B comprises a solid solution containing Cu and Si, and a solid solution containing Cu and Sn.
 8. The negative electrode material for non-aqueous electrolyte secondary batteries in accordance with claim 1 or 2, wherein said solid phase A comprises Si and said solid phase B comprises a solid solution or an intermetallic compound, which contains Ti and Si.
 9. The negative electrode material for non-aqueous electrolyte secondary batteries in accordance with claim 8, wherein said solid phase B comprises TiSi₂ having a crystal structure of at least one selected from the group consisting of Cmcm and Fddd.
 10. A non-aqueous electrolyte secondary battery comprising a positive electrode capable of a reversible electrochemical reaction of lithium, a non-aqueous electrolyte comprising an organic solvent and a lithium salt dissolved in said organic solvent, and a negative electrode comprising the negative electrode material in accordance with any of claims 1 to
 9. 